1. Field of the Invention
The invention pertains to a vibration damper with stroke-dependent damping force of the type having a cylinder filled with damping medium and a piston rod connected to a piston in the cylinder, the piston separating the cylinder into a working space on the piston rod side and a working space away from the piston rod, the piston having at least one first through-channel with a respective at least one outlet for flow in a first direction. A bypass connects the working space on the piston rod side to the working space away from the piston rod as a function of the position of the piston in the cylinder. A first valve disk covers the outlet of the at least one first through-channel, the first valve disk being movable from a closed position to an open position and having a first pressure-actuated surface which is exposed to pressure via said at least one through channel.
2. Description of the Related Art
A piston-cylinder assembly with distance-dependent damping force characteristics is known from U.S. Pat. No. 5,971,117. The piston rod of the piston-cylinder assembly carries two pistons a certain distance apart, each of which can generate a damping force in either direction of piston rod movement. At least one bypass groove, which is longer in the axial direction than the distance between the piston rings of the two pistons, is formed in the cylinder of the piston-cylinder assembly. Thus, three different performance characteristics are produced. When both pistons are present in the stroke range within which the bypass groove extends, the damping force is determined by the cross section of the bypass groove. As the distance traveled by the piston rod increases, one of the pistons moves beyond the bypass groove, and an intermediate characteristic is obtained. As soon as the second piston has also left the area of the bypass groove, the hardest damping force characteristic goes into effect. For a vibration damper which is variable in this way, however, two pistons with at least four valve disks and possibly valve springs are required. This expense can be too high for certain concrete applications.